fix: use system libelf-static on Alpine, vendored-libelf only on Ubuntu

vendored-libelf (libbpf-sys) calls make_elfutils() which runs
elfutils' autoconf configure.  That configure calls
  AC_SEARCH_LIBS([argp_parse], [argp])
  AC_SEARCH_LIBS([fts_close],  [fts])
Both argp and fts are GNU/BSD extensions absent from musl libc, causing
a hard configure error on Alpine.  argp-standalone fixes the first but
fts_close is still missing, making this a whack-a-mole problem.

Root cause fix:
- Alpine 3.20 ships libelf-static which is already musl-compiled WITHOUT
  zstd.  vendored-libelf is unnecessary there.  Use the system .a.
- Ubuntu 24.04 ships a glibc libelf.a compiled WITH zstd (unusable for
  musl targets), so vendored-libelf IS required.  Ubuntu glibc provides
  both argp_parse and fts_close, so configure succeeds.

Changes:
* Cargo.toml: move vendored-libelf out of libbpf-sys default features;
  add optional edriver feature 'vendored-libelf' that proxies to
  libbpf-sys/vendored-libelf.
* Makefile: add CARGO_EXTRA_FEATURES variable (default empty);
  append it to --features= in build/debug/test targets.
* CI yaml:
  - x86_64/Alpine: add libelf-static package; remove argp-standalone
    and all autotools no longer needed.
  - aarch64/Ubuntu: set cargo_extra_features=',vendored-libelf'.
  - Pass CARGO_EXTRA_FEATURES env in Build and Test steps.
  - Bump cache key to v4.

Author: chriskaliX

.github/workflows/ci-edriver.yaml

@@ -32,6 +32,8 @@ jobs:
             # zlib-static installs libz.a to /lib (not /usr/lib) on Alpine 3.20.
             lib_path: /lib:/usr/lib
             extra_cflags: ""
+            # Alpine libelf-static is musl-native, no zstd dep: no vendored-libelf.
+            cargo_extra_features: ""
           - arch: aarch64
             runner: ubuntu-24.04-arm
             target: aarch64-unknown-linux-musl
@@ -41,8 +43,12 @@ jobs:
             cc: musl-gcc
             lib_path: ""
             # musl-gcc uses -nostdinc; re-add system includes so vendored
-            # elfutils and libbpf can find kernel headers (linux/bpf.h etc.).
+            # libbpf can find kernel headers (linux/bpf.h etc.).
             extra_cflags: "-I/usr/include -I/usr/include/aarch64-linux-gnu"
+            # Ubuntu libelf is glibc-compiled: must vendored-compile elfutils.
+            # elfutils configure needs argp+fts which exist on glibc (Ubuntu) but
+            # not on musl (Alpine), hence this is Ubuntu-only.
+            cargo_extra_features: ",vendored-libelf"
     steps:
       # ── Alpine (x86_64) ─────────────────────────────────────────────────
       # Install BEFORE actions/checkout so git/bash/curl are available for
@@ -54,12 +60,10 @@ jobs:
             bash curl git \
             build-base linux-headers \
             clang llvm \
-            elfutils-dev \
+            elfutils-dev libelf-static \
             zlib-dev zlib-static \
             protobuf-dev \
-            pkgconf \
-            autoconf automake libtool gettext-dev flex bison gawk perl \
-            argp-standalone
+            pkgconf
 
       # ── Ubuntu (aarch64) ────────────────────────────────────────────────
       - name: Install build dependencies (Ubuntu / aarch64)
@@ -94,8 +98,8 @@ jobs:
           path: |
             ~/.cargo/registry
             ~/.cargo/git
-          key: ${{ matrix.arch }}-cargo-edriver-v3-${{ hashFiles('plugins/edriver/Cargo.lock') }}
-          restore-keys: ${{ matrix.arch }}-cargo-edriver-v3-
+          key: ${{ matrix.arch }}-cargo-edriver-v4-${{ hashFiles('plugins/edriver/Cargo.lock') }}
+          restore-keys: ${{ matrix.arch }}-cargo-edriver-v4-
 
       - name: Verify toolchain
         run: |
@@ -108,19 +112,19 @@ jobs:
           cd plugins/edriver && make build
         env:
           PLATFORM: ${{ matrix.arch }}
-          # vendored-libelf built with --without-zstd → no libzstd needed.
-          # vendored-zlib compiled from source → no system libz.a needed.
-          # lib_path is a fallback search path (libz.a on Alpine is in /lib).
+          # x86_64 Alpine: system libelf-static is musl-native (no zstd).
+          # lib_path covers /lib where Alpine's zlib-static installs libz.a.
           LIBBPF_SYS_LIBRARY_PATH: ${{ matrix.lib_path }}
-          # Kernel headers for vendored C compilation inside musl-gcc -nostdinc.
+          # aarch64 Ubuntu: musl-gcc -nostdinc needs kernel headers explicitly.
           LIBBPF_SYS_EXTRA_CFLAGS: ${{ matrix.extra_cflags }}
           # Override .cargo/config.toml [env] which defaults to "musl-gcc".
           CC_x86_64_unknown_linux_musl: ${{ matrix.cc }}
           CC_aarch64_unknown_linux_musl: ${{ matrix.cc }}
           CARGO_TARGET_X86_64_UNKNOWN_LINUX_MUSL_LINKER: ${{ matrix.cc }}
           CARGO_TARGET_AARCH64_UNKNOWN_LINUX_MUSL_LINKER: ${{ matrix.cc }}
-          # No -lzstd link arg needed: vendored elfutils is --without-zstd.
           RUSTFLAGS: "-C target-feature=+crt-static"
+          # Activates vendored-libelf only on Ubuntu aarch64 (see matrix).
+          CARGO_EXTRA_FEATURES: ${{ matrix.cargo_extra_features }}
 
       - name: Test
         run: |
@@ -135,3 +139,4 @@ jobs:
           CARGO_TARGET_X86_64_UNKNOWN_LINUX_MUSL_LINKER: ${{ matrix.cc }}
           CARGO_TARGET_AARCH64_UNKNOWN_LINUX_MUSL_LINKER: ${{ matrix.cc }}
           RUSTFLAGS: "-C target-feature=+crt-static"
+          CARGO_EXTRA_FEATURES: ${{ matrix.cargo_extra_features }}

plugins/edriver/Cargo.toml

@@ -7,13 +7,13 @@ description = "Rust version of hades edriver"
 
 [features]
 debug = ["sdk/debug"]
-# The `static` feature chains to libbpf-rs/static → libbpf-sys/static, which
-# links the system libelf.a.  On Ubuntu 24.04+ that libelf.a is compiled with
-# USE_ZSTD and references ZSTD_* symbols.  libbpf-sys does NOT emit
-# `cargo:rustc-link-lib=zstd`, so we must add `-lzstd` manually in
-# .cargo/config.toml ([build].rustflags for host build-scripts, and
-# [target.*-musl].rustflags for the final binary).
 static = ["libbpf-rs/static"]
+# Enable vendored elfutils compilation via libbpf-sys.
+# Only needed on glibc hosts (Ubuntu) where the system libelf.a is compiled
+# with USE_ZSTD.  On Alpine/musl the system libelf-static is already
+# musl-native and zstd-free, so this is unnecessary (and won't build on musl
+# because elfutils configure requires glibc-only argp/fts).
+vendored-libelf = ["libbpf-sys/vendored-libelf"]
 
 [dependencies]
 anyhow = "1.0"
@@ -31,7 +31,11 @@ libbpf-rs = { version = "0.26.2", features = ["static"] }
 # compiled with glibc headers (_FORTIFY_SOURCE=2), which generates
 # __snprintf_chk / __vsnprintf_chk calls that musl doesn't provide.
 # Compiling zlib from source with musl-gcc uses musl headers and avoids these.
-libbpf-sys = { version = "1.7", features = ["vendored-zlib", "vendored-libelf"] }
+# vendored-zlib: compile zlib from source so the .a is musl-compatible on
+# both Alpine and Ubuntu.  vendored-libelf is NOT listed here; it is gated
+# behind the optional `vendored-libelf` feature above and activated only on
+# glibc CI (ubuntu:24.04 aarch64) via CARGO_EXTRA_FEATURES in the Makefile.
+libbpf-sys = { version = "1.7", features = ["vendored-zlib"] }
 bitflags = "2.11.1"
 moka = { version = "0.12", features = ["sync"] }
 sdk = { path = "../../SDK/rust" }

plugins/edriver/Makefile

@@ -1,5 +1,9 @@
 # SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
 CMD_CLANG ?= clang
+# Extra cargo features appended to every --features= flag.
+# Set to ",vendored-libelf" on glibc hosts (ubuntu aarch64 CI) where the
+# system libelf.a is glibc-compiled and vendored compilation is required.
+CARGO_EXTRA_FEATURES ?=
 
 LIB_PATH := ../libs
 LIBBPF_CFLAGS = "-fPIC"
@@ -28,14 +32,14 @@ build: \
 	headers/libbpf/libbpf.a
 
 	cargo fmt
-	cargo build --release --bin edriver --target $(PLATFORM)-unknown-linux-$(LIBC) --features=static
+	cargo build --release --bin edriver --target $(PLATFORM)-unknown-linux-$(LIBC) --features=static$(CARGO_EXTRA_FEATURES)
 
 debug: \
 	headers/libbpf/libbpf.a
 
 	cargo fmt
-	cargo build --release --bin edriver --target $(PLATFORM)-unknown-linux-$(LIBC) --features=static,debug
+	cargo build --release --bin edriver --target $(PLATFORM)-unknown-linux-$(LIBC) --features=static,debug$(CARGO_EXTRA_FEATURES)
 
 test:
 	cargo fmt
-	cargo test --target $(PLATFORM)-unknown-linux-$(LIBC) --features=static,debug -- --include-ignored --show-output
+	cargo test --target $(PLATFORM)-unknown-linux-$(LIBC) --features=static,debug$(CARGO_EXTRA_FEATURES) -- --include-ignored --show-output